Generally, the wireless communication device of FDMA (Frequency-Division Multiple Access) type, and SCPC (Single Channel Per Carrier) type has employed ET (Envelope Tracking) method for the purpose of reducing power consumption.
The ET method is designed to change the power supply voltage of the power amplifier of the transmitter in accordance with output power of the power amplifier. For example, the envelope information (Envelope) is taken from the modulation signal, in accordance with which the power supply voltage of the power amplifier is changed. This allows the power amplifier to be operated in the nearly saturated state. The method may improve efficiency of the power amplifier and lessen the power loss compared with the case where the power supply voltage is fixed.
Meanwhile, generally, the wireless communication device of TDMA (Time-Division Multiple Access)/TDD (Time Division Duplex) type does not employ the ET method because of the following reasons. Firstly, the ET method is employed for the power amplifier of the transmitter, and the transmission time period for the device of TDMA/TDD type is shorter than that of FDMA type and SCPC type. The resultant effective power consumption of the power amplifier is low. For example, the transmission time period in the case of the device of TDMA/TDD type is 25% of the transmission time period in the case of the device of SCPC type which constantly executes transmission. Accordingly, the power consumption of the device of TDMA/TDD type becomes 25% of that of the device of SCPC type.
Secondly, the ET power source unit for supplying power to the power amplifier has to be provided in addition to the generally employed power source unit so as to use the ET method for the power amplifier. The space occupied by the ET power source unit in the mobile type wireless communication device may interfere with size reduction of such wireless communication device. For example, the generally employed power source unit includes a transmission power source unit for supplying power to the transmission circuit, a receiving power source unit for supplying power to a receiving circuit, and a control power source unit for supplying power to a control circuit.
Due to the above reasons, the device of TDD type does not employ the ET method. Recently, however, extension of the battery operable time has been increasingly viewed as important for the portable wireless communication device represented by the mobile wireless device from the disaster prevention perspective. Therefore, power consumption reduction is also viewed as important for the wireless communication device of TDD type.
The following patent literature 1 describes the technology for improving power efficiency by supplying power from the ET power source unit to the power amplifier of the transmitter.